• Preheat the oven to 350℉. Line a 9-inch square baking pan with parchment paper, letting a little hang from the sides for easy removal later.

To Make The Crumb Topping:

• In a medium bowl, combine cinnamon, salt, brown sugar substitute, and flour.
• Cut in the butter using two knives or a pastry blender until well combined. The mixture should resemble coarse breadcrumbs.
• Toss in the 1 cup of blueberries. Set aside.

To Make The Cake:

• Into a medium bowl, sift flour, baking soda, baking powder, and salt.
• In the bowl of an electric mixer fitted with the paddle attachment, cream butter and sweetener until light and fluffy, about 4 minutes.
• Add eggs, one at a time, until well combined. Add vanilla and beat until combined.
• Add the dry ingredients and the sour cream. Beat just until well combined. Fold in the 2 cups of the blueberries.
• Transfer the batter to the prepared pan. Sprinkle the crumb topping over the batter.
• Bake until golden brown and a toothpick comes out clean, approximately 50 to 60 minutes.
• Allow to cool in the baking pan for 1 hour. Slice and serve.